Eucalyptus biomechanical pulping process

ABSTRACT

In a new process for preparing pulped wood chips for paper making, chips from a hardwood such as eucalyptus are inoculated with aliving culture of one or more white rot fungi. The fungi propagate throughout the body of the wood chip, selectively attacking the lignin of the wood without harming the cellulosic fibers. Subsequent mechanical pulpting results in reduced utilization of energy, improved strength, and reduced cooking time.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] Not applicable.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0002] Not applicable.

BACKGROUND OF THE INVENTION

[0003] In the manufacture of paper from wood, the wood is first reducedto an intermediate stage in which the wood fibers are separated fromtheir natural environment and transformed into a viscous liquidsuspension known as a pulp. There are several classes of techniqueswhich are known, and in general commercial use, for the production ofpulp from various types of wood. The simplest in concept of thesetechniques is the so-called refiner mechanical pulping (RMP) method, inwhich the input wood is simply ground or abraded in water through amechanical milling operation until the fibers are of a defined desiredstate of freeness from each other. Other pulping methodologies includethermo-mechanical pulping (TMP), chemical treatment withthermo-mechanical pulping (CTMP), chemi-mechanical pulping (CMP) and theso-called kraft or sulfate process for pulping wood. In all of theseprocesses for creating pulps from wood, the concept is to separate thewood fibers to a desired level of freeness from the complex matrix inwhich they are embedded in the native wood.

[0004] Of the constituents of wood as it exists in its native state, thecellulose polymers are the predominate molecule which is desired forretention in the pulp for paper production. The second most abundantpolymer to cellulose in the native wood, which is the least desirablecomponent in the pulp, is known as lignin. Lignin is a complexmacromolecule of aromatic units with several different types ofinterunit linkages. In the native wood, lignin physically protects thecellulose polysaccharides in complexes known as lignocellulosics, andthose lignocellulosics must be disrupted for there to be marked enzymeaccessibility to the polysaccharides, or to separate lignin from thematrix of the wood fibers.

[0005] It has been suggested that biological systems can be utilized toassist in the pulping of wood. A desirable biological system would beone which is intended to liberate cellulose fibers from the ligninmatrix by taking advantage of the natural abilities of a biologicalorganism. Research in this area has focused on a type of fungi referredto as white-rot wood decay fungi. These fungi are referred to aswhite-rot, since the characteristic appearance of wood infected by thesefungi is a pale color, which color is the result of the depletion oflignin in the wood, the lignin having been degraded or modified by thefungi. Since the fungi appear to preferentially degrade or modifylignin, they make a logical choice for fungi to be utilized inbiological treatments to pulp wood, referred to as biopulping.

[0006] Several reports have been made of attempts to create biopulpingsystems using white-rot fungi on a variety of wood fibers. Previousresearch has concentrated on a single, or relatively few, species offungi. The most commonly utilized fungi in such prior systems is thewhite-rot fungi Phanerochaete chrysosporium, also referred to asSporotrichum pulverulentum. Other fungi which have been previously usedin such procedures include fungi of the genera Polyporus and Phlebia.The prior art is generally cognizant of the fact that attempts have beenmade to use biological organisms, such as white-rot fungi, as part of aprocess of treating wood, in combination with a step of eithermechanical or thermal mechanical pulping of cellulose fiber.

[0007] The use of white rot fungi for the biological delignification ofwood was studied as early as the 1950s at the West Virginia Pulp andPaper Company (now Westvaco) (Lawson and Still, C. N. (1957) Tappi J.,40, 56A-80A). In the 1970s Eriksson and coworkers at STFI (SwedishForest Product Laboratory) demonstrated that fungal treatment couldresult in significant energy savings for mechanical pulping (U.S. Pat.No. 3,962,033 for an invention by Eriksson et al. (1976); (Ander andEriksson, K. E., (1975); Svensk Papperstidning, 18, 641) (Eriksson andVallander, K. E. (1982) Svensk Paperstidning, 85(6), R33-R38). Twosequential biopulping consortia comprised of the USDA Forest Service,Forest Products Laboratory in Madison, Wis. (hereinafter, “FPL”), theUniversities of Wisconsin and Minnesota, and 22 pulp and paper andallied companies demonstrated the techno-economic feasibility ofbiopulping in connection with mechanical refining (Akhtar et al.,(1992a), Tappi J., 75(2), 105-109); (Akhtar et al., (1992b)Biotechnology in the pulp and paper industry, (Kuwahara, M. and Shimada,M. eds.) Tokyo, UNI Publishers Company Ltd., p. 545); (Akhtar et al.,(1993) Holzorschung, 47(1), 36-40); (Blanchette, R., (1984) Applied &Environmental Microbiology, 48(3), 647-653); (Blanchette et al., (1988)Biomass, 15, 93-101); Leatham et al.(1989) Biotechnology in the Pulp andPaper Industry, 4^(th) International Symposium, Raleigh, N.C., May16-19); (Leatham et al., (1990a), Tappi J., 73(3), 249-255); Leatham etal., (1990b), Tappi J., 73(5), 197-200), (Myers et al., (1988), TappiJ., 71(5), 105-108); (Pearce, N. H., et aL) screened 204 isolates ofwood decay fungi in bench scale trials for their performance inbiomechanical pulping of eucalyptus chips. (Proccedings 49^(th) AppitaAnnual General Conference, Hobart, Tasmania, Australia, 2-7 Apr. 1995,347-351) Refining energy savings of 40%-50% were obtained with someselected fungi. No strength improvements were reported. Additionaldevelopments in biomechanical pulping were described in: U.S. Pat. No.5,055,159 for an invention by Blanchette, et al. (1991); U.S. Pat. No.5,460,697 for an invention by Akhtar et aL (1995); U.S. applicationpublished as WO 9605362 on Feb. 1, 1996.

[0008] Unfortunately, biomechanical processes have only gained limitedcommercial acceptance, and have not been widely utilized. One of thedifficulties has been that most of the prior techniques for utilizingbiological techniques for the pulping of paper have resulted in paperwhich has had only marginal strength increase or is weaker than papersmade by more conventional processes.

[0009] In fact, while a certain amount is known about the interaction oflignin and cellulose in wood fibers, because of the extreme complexityof the relationships, and the variation in the enzymes produced byvarieties of the white-rot fungi, it is not readily possible to predictfrom the action of a given fungus on a given type of wood whether or notthe paper made from wood partially digested with such fungus will havedesirable qualities or not. The selection of white-rot fungi forbiopulping applications on the basis of selective lignin degradation mayseem a rational one, but it has proven to be a poor predictor of thequality of the resultant paper. The exact relationship between thedegradation of lignin, and the resulting desirable qualities of paperproduced at the end of the pulping process, are not at all clear.Accordingly, given present standards of technology and the presentunderstanding of the complex interaction of lignin and cellulose, it isonly possible to determine empirically the quality of paper producedthrough a given biological pulping process and the amount of any energysavings achieved through such a process.

[0010] For reasons set forth above, most of the fungi screened for thebiomechanical pulping of one type of wood do not necessarily work wellin the biomechanical pulping of another type of wood. All thebiomechancial pulping references described above are directed to thebiopulping and processing of wood species other than eucalyptus, a verycommon wood species in many parts of the world and potentially valuablesource of pulp for papermaking or other processes. What is needed is amethod of processing eucalyptus wood which takes advantage of the costsavings of mechanical pulping techniques without a loss of end productquality one often experiences when using mechanical pulping.

SUMMARY OF THE INVENTION

[0011] In the method of the present invention, eucalyptus wood ispartially degraded with a culture of the fungus Ceriporiopsissubvermispora, followed by mechanical pulping of the treated wood.

[0012] It has been found that through the biological degradation ofeucalyptus chips using Ceriporiopsis subvermispora followed bymechanical pulping of the treated wood chips, a dramatic decrease in theenergy required for mechanical pulping is achieved while at the sametime giving rise to paper which has enhanced, rather than decreased,strength characteristics.

[0013] It is thus an advantage of the process described in accordancewith the present invention that a procedure for the biomechanicalpulping of eucalyptus wood chips is described which utilizes less energythan prior art techniques and which results in paper having moredesirable strength characteristics.

[0014] It is further an object of the present invention in that itutilizes a natural biological organism to degrade the wood thus reducingthe likelihood of unwanted artificial environmental contaminantsproduced by degradation of lignin and its byproducts.

[0015] It is a further advantage of the present invention in that it hasbeen found that the biological processing of the wood chips inaccordance with the present invention can be done in a staticfermentation procedure without the need for an exotic or movingfermenting chamber thereby allowing the process to be used morepractically on a large scale.

[0016] Other objects, advantages, and features of the present inventionwill become apparent from the detailed description of the invention,below.

DETAILED DESCRIPTION OF THE INVENTION

[0017] The present invention is directed toward the biologicalpretreatment of wood chips for pulp making for paper manufacture. It hasbeen particularly found here that through the use of a particularspecies of fungus, and the maintenance of relatively forgivingconditions during the treatment of wood chips by said fungus, it ispossible to utilize a biological treatment or pretreatment as a part ofa process of pulping eucalyptus wood, a wood resource of high commercialimportance in many parts of the World. It has further been found thatthe pulping process results in a paper which has a strength which isincreased over paper made from eucalyptus wood by purely mechanicalpulping and over paper made from other species of wood by biomechanicalpulping. It has been found, furthermore, that the eucalyptusbiomechanical pulping method of the present invention results in adramatic savings in the energy expended during the mechanical pulpingprocess. In other words, the process of biomechanical pulping ofeucalyptus wood of the present invention not only results in energysavings; it also results in a stronger product.

[0018] This process of the present invention makes use of white rotfungi, preferably, a culture of C. subvermispora, more preferably aculture of C. subvermispora L-14807-SS-3. However, other white rot fungican also be used. Strains of C. subvermispora can be maintained byconventional fungal culture techniques most conveniently by growing onpotato-dextrose-agar (PDA) slants. Stock slants may routinely beprepared from an original culture for routine use and may berefrigerated until used. The particular strain of C. subvermisporautilized in the examples below, L-14807-SS-3 was obtained from theCenter for Mycology Research, Forest Products Laboratory, Madison, Wis.It was found that particular strain of fungus was particularlywell-suited for biomechanical pulping of eucalyptus wood, according tothe process of the present invention. However, other it is contemplatedthat other strains of C. Subvermispora, such as—CZ-3, L-9186-SP,FP-105732, and FP-105752-SS5, and other white rot fungi, such asHyphodontia setulosa, Phlebia subserialis, Phlebia brevispora, Phlebiatremellosa, Phanerochaete chrysosporium would be suitable for use in themethods of the present invention.

[0019] The process of the present invention is intended for andparticularly adapted for the biopulping of eucalyptus. The wood isconverted to chips through a conventional technology. Wood chips areheat treated, preferably with steam, to disable but not necessarilysterilize the chips prior to inoculation with the fungus. The moisturecontent in the chips is kept at fiber saturation point or greater. Apreferred moisture content would be approximately 50-55% of the totalwood based on wet weight basis of the chips.

[0020] Fungi are preferably applied to the wood as follows. To inoculatesignificant volumes of wood chips, a starter inoculum may be prepared.PDA plates are inoculated from PDA slants and incubated at 27±1° C. and70-90% relative humidity. These plates are used to inoculate 1 literErlenmeyer flasks containing potato dextrose broth and yeast extract.The inoculated flasks are incubated without agitation in an incubator at27±1° C. and 70-90% relative humidity for 7-10 days. The surface of themedium is covered with the fungus in the form of mat. The fungal mat isremoved from the medium, washed with sterilized water on sterilizedbuchner funnel to remove all the medium. The fungal mat is transferredinto a sterile waring blender with sterile forceps and blended withsterile water. This suspension is used to inoculate wood chips. Scalingup the foregoing culture steps for preparing the fungal inoculationinvolves preparation of media in commercial scale vats, and growth offungi in commercial scale fermenters. Using industrial scale equipment,fungal cultures in 500-1500 gallon batches are readily obtainable.

[0021] Fungal treatment of wood chips is carried in bioreactor which maybe any of a number of styles capable of handling solid mediafermentation culture. It is merely required that the stationary or solidphase reactor have sufficient aeration so as to ensure adequate O₂ flowto the fungus and significant removal of CO₂ therefrom. In fact, it isan advantage of the process that it can be conducted in staticfermentation procedure without the need for an exotic or movingfermenting chamber thereby allowing the process to be used morepractically on a large scale. Aeration, humidity and temperature are allpreferably controlled, to at least some extent. On an industrial scale,the inoculated chip mass may be incubated in cylindrical silos or inopen chip piles of 20-200 tons, under nonstick conditions, providedproper ventilation is maintained, as discussed more fully hereafter.

[0022] For the fungal treatment, wood chips are put in the bioreactor,autoclaved and cooled to room temperature, or exposed to steam todisable native microorganism populations without absolute sterilization.The wood chips to be treated are inoculated with starter culture. Theamount of inoculum added to the chips can vary. It should be sufficientto ensure growth and spread to all chips in the bioreactor. Inoculumlevel of 1 to 5 gm per ton of wood chips was found to be sufficient. Thechips so inoculated will then be incubated during a time period in whichthe fungal mycelia will penetrate throughout the wood chips. It has beenfound that nutrients are not required during fungal treatment ofeucalyptus wood chips. Addition of nutrients does not give additionalbiopulping benefits but result in more loss in the weight of wood chipsand unbleached pulp yield. The most desired temperature range depends onthe fungal strains.

[0023] It has been found that a bioreactor kept in the range of 27±2° C.with a moisture content in the wood of 55-65% achieves a great degree ofmycelia penetration of wood chips that results in significantdegradation of wood chips for paper pulping process. The wood chips areaerated continuously during the incubation period with the air saturatedwith moisture that the wood maintains the constant moisture content ofabout 55-65%. It has been found that under the conditions usedexperimentally, an incubation period of 1 to 3 weeks results insignificant modification of the wood chips and reduction in energyoutput for mechanical processing in the subsequent processing steps.

[0024] The biologically degraded wood chips are then subjected to amechanical pulping process. Eucalyptus pulp made according to thebiomechanical pulping procedure of the present method can then bebleached in a multistage bleaching process and made into paper usingstandard paper-making techniques. Paper made from eucalyptusbiomechanical pulp is better in quality, strength and texture to thatcreated from eucalyputs through a simple mechanical pulping process andto that created from other woods through either simple mechanical orbiomechanical pulping processes.

[0025] Effective biopulping can be carried out under nonsterileconditions in which naturally occurring flora are present and viable.However, better results are obtained with steamed or autoclaved woodchips. Eucalyptus wood chips are exposed to live steam resulting inelevating their surface temperature to about 90° to 100° C., as measuredimmediately after steam treatment. The exposure time is a function ofthe temperature of the superheated vapor and also the inlet pressure.While 101° to 108° C. influent steam at 15 to 75 in line psi forexposure times of 3 to 50 seconds is adequate, the optimum values arebest determined in a few empirical process runs for the particular typeand configuration of equipment, as hereinafter described in more detail.

[0026] The chamber in which steam treatment takes place should not betoo tightly packed. Open space of about under 10% to over 65% of thevolume capacity is sufficient to allow penetration of steam to all chipsurfaces provided that the chips can be mechanically turned or agitatedto prevent impeded exposure to steam at touching surfaces. For example,in the screw conveyor used in a preferred embodiment of the invention,the open space above the chips in the conveyor was found to beapproximately 57% to 69%. In addition, the void space between the chipsin the preferred embodiment amounted to approximately 61%. Therefore,the total void space in the conveyor amounted to approximately 83%(large chips) to 88% (small chips). Uniformity of steam treatment isvery important, as the naturally occurring flora must be uniformlydisabled or biosuppressed physiologically to avoid spots of overgrowthby contaminants during the subsequent incubation step.

[0027] A particularly efficient method of steam treatment is byinjecting steam into a continuous flow screw or auger bearing the chipsat about 30% to 45% spacial density as discussed above. It was foundthat exposure time of chips adequate for the present process could beonly 40 seconds compared to 5-10 minutes in a quiescent batch mode.Steam was released at moderate pressure and applied ambiently withoutpressurizing the vessel.

[0028] A number of species of contaminating organisms can readily beisolated from moistened wood chips including Aspergillis spp.,Colletotrichum spp., Trichoderma spp., Gliocladium spp., Ophiostomaspp., Penicillium spp., Ceratocystis spp., Nectria spp., Cytospora spp.,and Alternaria spp. Many of these are more physiologically robust andfaster growing than the inoculating lignin-degrading or modifying fungiof choice. Growth of these organisms is also enhanced in many instancesby the nutrient adjuvants contained in the fungal inoculum. Therefore,addition of such nutrients is avoided.

[0029] Once the indigenous, undesirable microbes are disabled orsuppressed by steam treatment, the less robust and more fastidiouswhite-rot fungi in the inoculum are able to remain dominant overextended periods. The disabled organisms are still viable and capable ofbecoming dominant, as shown by biopulping runs in which the treatmenttemperature was inadvertently allowed to rise only to sub-optimallevels. In those instances the runs were ruined by overgrowth of thecontaminating fungi. Clearly a highly delicate but controllable processbalance must be maintained, but it is unclear scientifically whatcompetitive factors are at work to maintain the desired biologicalbalance over extended incubations. Reducing exposure to steam to aminimum without sterilization also has favorable implications forprocess costs. The low exposure time conductive to a continuoustreatment means that high volume treatment required in any commercialscale process is attainable in the present invention.

[0030] If steam or heat is used to sterilize the wood chips, the chipsare preferably cooled prior to inoculation of the biopulping fungi tominimize the possiblity of killing or disabling the organisms in theinoculum. Chips steam treated on a continuously moving path are passedthrough heat transfer means which cool the chips to an appropriatetemperature for inoculation. Applicants have found that the most costeffective and simplest method is to place an in-line air blower manifolddirectly in the conveyance path, and adjust the air flow to a rate thatwill cool the passing chips adequately.

[0031] Chips to be inoculated with Ceriporiopsis subvermispora L14807SS-3 are preferably cooled to no more than about 50° C., more preferablyto a temperature between about 40° C. and about 45° C. The highesttemperature tolerated by biopulping organisms will vary from species tospecies or even from strain to strain of the same species, so thatempirical tests may be necessary to determine a physiologically suitabletemperature for inoculation of wood chips with any given type ofculture. Cooling only to the highest physiologically suitabletemperature minimizes the cooling time and speeds the process, andreduces the energy consumed.

[0032] Inoculation of the biopulping fungi is preferably carried outin-line, and applied as a liquid spray to the passing wood chips. As inthe steam treatment, the working action of agitated conveyor or augerallows inoculum to be uniformly adsorbed onto the chip surfaces bytumbling and churning during rotary or other agitated conveyance. It isimportant that the inoculum be applied substantially thoroughly anduniformly to the chip surfaces. If the biopulping fungi are to maintaindominance over other flora, the contaminating flora should not be givena sufficient opportunity to reestablish themselves in local areas of thechip surfaces where coverage of inoculum is uneven.

[0033] The enzymatic breakdown or modification of lignin by fungi is anexothermic reaction, so that when a large mass of chips is undergoingdelignification, a substantial concentration of heat ensues. As thesurface area of the mass of chips diminishes relative to the total mass,the problem intensifies since wood itself is an excellent heatinsulator. The most practical way to dissipate heat in the chips toprevent the temperature from exceeding the level at which the biopulpingfungi are killed, and the contaminants begin to overgrow the fungi, isby forcing air through the chips.

[0034] It has been found that the temperature of chip piles can beadequately controlled and maintained at levels biocompatible with thecontinued propagation and dominance of the fungus by loading the chipsonto an air pervious frame defining a plurality of ducts through whichforced air is passed. It has been empirically determined that thehumidity of the air should be in a range from at least 30% up to over95% relative humidity, preferably about 85%, and the flow rate should beadjusted seasonally to maintain the temperature in the core of the pilewithin the active growth range of the fungus, which must be determinedfor each species. In the case of C. subvermispora, the range isapproximately 27° to 32° C.

[0035] After inoculation, the chips may be conveniently collected inlarge piles. Temperature and humidity control are important for optimalfungal propagation and lignin degradation or modification. It has beendetermined that practical control can be maintained for piles loadedonto the bottom frame referred to above having dimensions about 40-55feet high, 100 feet wide and any length. Two 400 foot long piles canaccommodate a pulp plant utilizing 600 tons of chips daily. To obtainproper humidity, wet bulb/dry bulb tests can be performed on theinfluent air. Relative humidity should preferably be maintained at about70%-90%. Humidification of air by conventional means such as foggingprior to pumping or fanning into the frame ducts is generally necessary.The amount of heat generated in the pile generally requires continuousdissipation by forced air flow even during the winter months in thenorthern climes.

[0036] Incubation times are related to the degree of lignin digestion ormodification desired, the type of wood chips being handled, and theparticular fungus or combination of fungi being utilized in the process.Useful periods of incubation range from a few days to four weeks. On theother hand, prolonged incubation results in larger standing inventoriesof chips and larger on site storage capacity.

[0037] Tubular reactors (silo reactors) can also be used for biopulping.This silo reactor has a large-scale (multiton) capacity. A perforatedplate at the bottom of the reactor supports the chips approximately 5 cmabove the bottom of the reactor. Air is supplied to this void space atthe bottom center of the reactor. A baffle plate immediately above theair inlet distributes the air more evenly across the bottom of thereactor.

[0038] After the incubation of the fungi in the wood chips, the woodchips are then preferably subjected to a conventional mechanicalrefining process to make wood pulp of the desired level of freeness.Dilution water is added to the chips and the chips are run through amechanical refiner through a number of passes. The number of passes ofthe chips/pulp mixture will depend upon the freeness desired for theparticular paper application to be made. The chip/pulp mixture is fedthrough the refiner until the desired level of freeness is achieved.Thus freeness may be periodically monitored to determine the progress ofthe pulps toward the freeness level which is desired for the paper.Between passes the wood pulp may be dewatered as necessary.

[0039] The biomechanical pulps made through this procedure may then bemade into paper using standard paper making techniques. It has beenfound that the standard techniques as described by the TechnicalAssociation of the Paper and Pulp Industry (TAPPI) which are known towork with mechanically refined pulps work equally well with thebiomechanically refined pulps of the type created by the processdescribed herein. Accordingly, the paper may be made in conventionalmethodologies. The paper from the biomechanically created pulp can becompared in quality, strength and texture to that created through simplemechanical pulping and it will be found that the biomechanically createdpulp has significantly increased strength properties. Thus it isapparent that the process of the present invention does not sacrificethe quality or strength of the paper in order to achieve the highlydesirable energy savings, but in fact results in a unique combination ofboth significant reduction in energy utilization in the process, and anincrease in the strength properties of the resulting paper.

[0040] Biomechanical pulping of eucalyptus wood according to the processof the present invention produces paper of surprisingly high qualitycompared to previous studies with other woods. In previous studies, wehave seen some improvements in paper strength properties duringbiomechanical pulping of both hardwood and softwood species with severalwhite-rot fungi (U.S. Pat. No. 5,750,005 “Method of Enhancing BiopulpingEfficacy,” Akhtar (1998)). For example, improvements were observed inburst index of up to 37% and tear index of up to 44% (see Table 1,below) with pine chips (softwood chips), and in tear index of up to 24%(see Table 2, below) with aspen chips (hardwood chips) processed bybiomechanical pulping using various species of white-rot fungi comparedto mechanical pulping without inoculation. Surprisingly, when eucalyptuswood chips were inoculated with Ceriporiopsis subvermispora, asdescribed in the Examples below, substantial improvements in paperstrength properties (burst index 70% and tear index 184%) were observed(see Table 3, below). TABLE 1 Biomechanical pulping of pine (softwood)chips with several white-rot fungi and strains (2-week treatment). %improvements over control Fungi/strain Burst index Tear index Phlebiabrevispora HHB-7099 0 13 Phlebia subserialis RLG 6074-sp 37 44Dichomitus squalens MMB 10963-sp 13 41 Hyphodontia setulosa FP 106976 040 Perenniporia medulla-panis HHB 12172 24 34 Ceriporiopsissubvermispora CZ-3 0 14 Ceriporiopsis subvermispora FP-105752 SS-4 0 14Ceriporiopsis subvermispora L-14807 SS-1 0 14 Ceriporiopsissubvermispora L-14807 SS-3 0 21 Ceriporiopsis subvermispora L-14807 SS-50 21 Ceriporiopsis subvermispora L-14807 SS-10 0 11

[0041] TABLE 2 Biomechanical pulping of aspen (hardwood) chips withseveral white-rot fungi and strains (2-week treatment). % improvementover control Fungi/strain Burst index Tear index Phlebia subserialis RLG6074-sp 0 0 Hyphodontia setulosa FP 106976 0 0 Phlebia brevispora HHB7099 0 19 Phlebia tremelosa FP 102557-sp 0 24 Ceriporiopsissubvermispora L-14807 SS-3 0 11

[0042] TABLE 3 Biomechanical pulping of Eucalyptus grandis (hardwood)chips with Ceriporiopsis subvermispora L-14807 SS-3 (2-week treatment).% improvement over control Burst index Tear index 70 184

[0043] Previous data with both hardwood and softwood species, includingthe data summarized in Tables 1 and 2, above, show strength improvementswith fungus-treated chips compared to the control. However, theseimprovements are not as pronounced as those obtained duringbiomechanical pulping of eucalyptus wood chips, shown in Table 3 and inthe Examples below. Eucalyptus is a hardwood species with poor paperstrength, due to short fiber length. Because of its poor paper strengthproperties, this wood has traditionally been considered to be of onlylimited use in the production of pulp utilized in mechanical pulpingprocesses. Therefore, traditionally, in the final furnish from whichnewsprint and tissue paper is produced, a significant amount of kraftpulp (about 50%) is mixed with eucalyptus mechanical pulp to impartstrength. Biomechanical pulping of eucalyptus wood according to theprocess of the present invention results in such a substantial increasein fiber strength that it is possible to significantly reduce the amountof kraft pulp required for a final furnish.

[0044] Biomechanical eucalyptus pulp behave more like a softwoodmechanical pulp, with the strength characteristics of such a pulp, thanit behaves like a traditional hardwood pulp. These highly unexpectedresults have only been observed with only eucalyptus wood. We haveevaluated other types of hardwood in the past, but never achieved suchimprovements in paper strength properties.

[0045] Details of the process of the present invention will become moreapparent from the following examples which illustrate laboratory-scaleembodiments on of the process of the present invention, and resultsachieved thereby.

EXAMPLES Example 1 Biomechanical Pulping of Eucalyptus Wood

[0046] Eucalyptus wood chips were supplied by a mechanical pulp mill inBrazil. Chips were placed in plastic bags and frozen to prevent thegrowth of contaminating microorganisms.

[0047] Bioreactors containing 1.5 kg of chips (dry weight basis) weresteam sterilized for 10 min. prior to inoculation. After cooling at roomtemperature, these chips were inoculated with a suspension containing,water, unsterilized corn steep liquor and fungus. The inoculatedbioreactors were incubated for 2 weeks at 27° C. and 65% relativehumidity. The control and fungus-treated wood chips were refined to apulp and then used to produce paper. The chips were heat treated withsteam pressurized to 15 p.s.i.g. for 1 minute and 15 seconds. Duringthis time, the chips were sent through a thermo-mechanical refiner(Sprout-Bauer, model # 1210P, having a plate pattern D2B505, and 300-mmdiameter) for fiberization. The pulp produced was subsequently fiberizedin a Sprout-Waldron Model D2202 single rotating 300 mm diameter diskatmospheric refiner. Pulp was collected at each pass as hot waterslurry. Between the passes the pulp slurry was dewatered toapproximately 25% solids in a porous bag by vacuum. Dilution water at85° C. was then added each time as the pulp was fed into the refiner.Samples of the pulp were taken and tested for the Canadian StandardFreeness (CSF) and the process continued until the samples were refinedto 300-500 CSF. Hand sheets were also prepared and tested using TAPPIstandard testing methods.

[0048] Fungal pretreatment of eucalyptus wood chips was found to enhancepaper strength properties substantially compared to the untreatedcontrol (see Table 4, below). The fungal pretreatment increased burstindex by 70%, tear index by 184%, tensile strength by 120% and breakinglength by 120% compared to the control. TABLE 4 Paper strengthproperties comparison. Strength properties Control (untreated) chipsFungus-treated chips Freeness (ml) 402 390 Burst index (kN/g) 0.20 0.34Tear index (mNm2/g) 1.03 2.93 Tensile strength (Nm/g) 5.16 11.35Breaking length (m) 526 1157

[0049] The results summarized above indicated that the treatedmechanically processed fibers were stronger than conventional mechanicalfibers.

Example 2 Replacement of 30% Kraft Pulp in a 50/50 Mechanica/Kraft Pulp

[0050] Most paper is generally produced from a furnish which is acombination of mechanical and chemical pulp, such as kraft pulp. Kraftpulp fibers are generally included in most papers because of their highstrength and low lignin content. Unfortunately, kraft pulp fibers areexpensive to produce. Kraft pulp is mixed with mechanical pulp to cutdown on costs of production. However, there is generally a limit to whatproportion of a pulp can comprise mechanical pulp fibers, withoutcompromising the quality of the paper produced therefrom.

[0051] In this Example, paper produced from untreated pulp samplesconsisting of 50% mechanical fibers plus 50% hardwood bleached kraftpulp fibers was compared to paper produced from fungus-treated pulpsamples consisting of 80% biomechanical fibers plus 20% hardwoodbleached kraft pulp fibers. The results of this study are summarized inTable 5, below. These results clearly indicate that at least 30% of theexpensive kraft fibers in a 50/50 mix of mechanical/kraft pulp can besubstituted with biomechanical pulp fibers, which are significantly lessexpensive than kraft pulp. The hardwood bleached kraft pulp fibers were100% hardwood, commercial grade, and were produced by a paper mill inBrazil. TABLE 5 Kraft substitution studies with pulp samples.Fungus-treated Strength properties Control (untreated) chips^(a)chips^(b) Burst index (kN/g) 0.35 0.38 Tear index (mNm²/g) 1.69 2.92Tensile strength (Nm/g) 9.40 11.26 Breaking length (m) 959 1148 Density(kg/m³) 310 307 Specific volume (cm³/g) 3.23 3.26 Drainage time (second)5 5

Example 3 Replacement of 40% Kraft Pulp in a 50/50 Mechanica/Kraft Pulp

[0052] Eucalyptus wood was pulped in separate portions as described inExamples 1-2, using mechanical or biomechanical pulping techniques.Paper was produced from a furnish of an untreated pulp of 50% mechanicalpulp, 40% hardwood bleached kraft pulp, and 10% softwood kraft pulp wasprepared as a control, above. Paper was also produced from a furnish oftreated pulp of 90% biomechanical ecucalyptus fibers and 10% softwoodfungus-treated kraft pulp, and compared to paper produced from thecontrol pulp. The results of this study are presented in Table 6, below.TABLE 6 Kraft substitution studies with pulp samples. Fungus-treatedStrength properties Control (untreated) chips^(a) chips^(b) Burst index(kN/g) 0.35 0.68 Tear index (mNm²/g) 2.50 3.83 Tensile strength (Nm/g)9.41 14.50 Breaking length (m) 960 1476 Specific volume (cm³/g) 3.023.17

[0053] The results of this study suggest the possibility of replacingeven 40% hardwood bleached kraft pulp with biomechanical fibers in ablend containing 50% kraft pulp fibers.

We claim:
 1. A biomechanical method of making a wood pulp fromeucalyptus wood comprising the steps of: (a) providing eucalyptus woodchips in a bioreactor; (b) inoculating the wood chips with an inoculumincluding a viable culture of Ceriporiopsis subvermispora; (c)incubating the wood chips under conditions favoring the propagation ofthe fungus through the wood chips for a sufficient amount of time forthe fungus to modify a significant amount of the lignin naturallypresent in the wood chips; and (d) mechanically pulping the wood chipsdegraded by the fungus into a paper pulp.
 2. The method of claim 1,wherein the culture of Ceriporiopsis subvermispora is a culture ofCeriporiopsis subvermispora L-14807 SS-3.
 3. The method of claim 1 whichincludes the further step of bleaching of the paper pulp by a knownmultistage bleaching process.
 4. The method of claim 1 wherein theincubation step is a static incubation step.
 5. The method of 1 whereinCeriporiopsis subvermisporais a strain selected from the groupconsisting of L-14807-SS-3, CZ-3, FP-105752-SS-5, FP-10572 andL-9186-SP.
 6. The method of claim 1 wherein the wood chips areinoculated with the fungus and known nutrients.
 7. The method of claim 1wherein moisture content of the wood chips prior to the step ofinoculation is kept at fiber saturation point or greater.
 8. The methodof claim 8 wherein said moisture content is 50-55% of the total woodbased on a wet weight of the chips.
 9. The method of claim 1 wherein thewood chips are inoculated with 1 to 5 gms inoculum/ton of wood.
 10. Themethod of claim 1 wherein moisture content in the wood during the stepof incubation is 55-65%.
 11. A method of making a wood pulp fromeucalyptus wood comprising the steps of: (a) chipping eucalyptus woodinto wood chips; (b) introducing the wood chips into a bioreactor; (c)inoculating the wood chips with an inoculum including a viable cultureof a white rot fungus; (d) incubating the wood chips under conditionsfavoring the propagation of the fungus through the wood chips for asufficient amount of time for the fungus to modify a significant amountof the lignin naturally present in the wood chips; and (e) mechanicallypulping the wood chips degraded by the fungus into a paper pulp.
 12. Themethod of claim 11 wherein said white rot fungus is Hyphodoutiasetulosa.
 13. The method of claim 11 wherein said white rot fungus isPhlebia subserialis.
 14. The method of claim 11 wherein said white rotfungus is Phlebia brevispora.
 15. The method of claim 11 wherein saidwhite rot fungus is Phlebia tremellosa.
 16. The method of claim 11wherein said white rot fungus is Phanerochaete chrysosporium.
 17. Amethod for producing paper comprising the steps of: (a) introducingeucalyptus wood chips into a reactor; (b) inoculating the wood chips inthe reactor with a starter inoculum of the fungus Ceriporiopsissubvermispora; (c) incubating the wood chips under conditions favorableto the propagation of the fungus through the wood chips; (d)mechanically pulping the incubated wood chips to a selected level offreeness of fibers in the pulp; and (e) making paper with the pulp soproduced.
 18. The method of claim 17, wherein the culture ofCeriporiopsis subvermispora is a culture of Ceriporiopsis subvermisporaL-14807 SS-3.
 19. The paper produced by the method of claim
 17. 20. Thepaper of claim 19 having at least a 70% improvement in burst index, andat least a 184% improvement in tear index over paper produced by amechanical pulping of eucalyptus wood without inoculation ofCeriporiopsis subvermispora.
 21. A method for producing paper comprisingthe steps of: (a) introducing eucalyptus wood chips into a reactor; (b)inoculating the wood chips in the reactor with a starter inoculum of thefungus Ceriporiopsis subvermispora; (c) incubating the wood chips underconditions favorable to the propagation of the fungus through the woodchips; (d) mechanically pulping the incubated wood chips to a selectedlevel of freeness of fibers in the pulp; and (e) making paper with thepulp produced, the paper having at least a 70% improvement in burstindex, and at least a 184% improvement in tear index over paper producedby a mechanical pulping of eucalyptus wood without inoculation ofCeriporiopsis subvermispora.
 22. A method for producing paper comprisingthe steps of: (a) introducing eucalyptus wood chips into a reactor; (b)inoculating the wood chips in the reactor with a starter inoculum of thefungus Ceriporiopsis subvermispora; (c) incubating the wood chips underconditions favorable to the propagation of the fungus through the woodchips; (d) mechanically pulping the incubated wood chips to a selectedlevel of freeness of fibers in the pulp; and (e) making paper with 80%of the eucalyptus pulp so produced and 20% of hardwood bleached kraftpulp.
 23. A method for producing paper comprising the steps of: (a)introducing eucalyptus wood chips into a reactor; (b) inoculating thewood chips in the reactor with a starter inoculum of the fungusCeriporiopsis subvermispora; (c) incubating the wood chips underconditions favorable to the propagation of the fungus through the woodchips; (d) mechanically pulping the incubated wood chips to a selectedlevel of freeness of fibers in the pulp; and (e) making paper with 90%of the eucalyptus pulp so produced and 10% of softwood fungus treatedkraft pulp.
 24. A method of producing paper comprising the steps of: (a)chipping eucalyptus wood into wood chips (b) heating the wood chips bysteam elevating the surface temperature of the wood; chips to about 90°C. to about 100° C. in a chamber having open space of about 10% to about65% of volume capacity; (c) cooling the wood chips to a temperaturebetween about 40° C. to about 45° C.; (d) inoculating the wood chips bya liquid spray of an innoculum including a viable culture ofCeriporiopsis subvermispora L-14807 SS-3; (e) incubating the wood chipsunder conditions favorable to the propagation of the fungus through thewood chips; (f) mechanically pulping the incubated wood chips to aselected level of freeness of fibers in the pulp; and (g) making paperwith the pulp produced, the paper having at least a 70% improvement inburst index, and at least a 184% improvement in tear index over paperproduced by a mechanical pulping of eucalyptus wood without inoculationof Ceriporiopsis subvermispora.